Mattress cores, for example, have previously included an array of strings individually pocketed springs. In such mattress cores, each spring coil is encased within its own fabric sack, which is usually made in the form of a pocket defined between two plies of a fabric strip connected together at intervals by transverse stitching. The two-ply strip is usually formed by folding a strip of double width upon itself along its longitudinal midline, leaving the overlapped plies along the unjoined opposite edge of the strip to be connected to each other to close the pocket after the spring is inserted.
A variety of techniques have evolved for the manufacture of pocketed springs. Some of these techniques teach the creation of the pockets within the fabric plies prior to insertion of the wire spring and others teach the insertion of the coaxially compressed wire springs between the plies of the strip and the subsequent creation of the pockets by stitching the two plies to each other along transverse lines between adjacent springs. In either technique, the pocket is closed after the insertion of the spring, usually be stitching the two plies together along a line parallel to the free edges of the plies.
U.S. Pat. No. 4,234,983 provides an example of an improved method of manufacturing a mattress core. Specifically, U.S. Pat. No. 4,234,983 teaches manufacture of an array of strings of pocket springs in which, for each string, the overlaid fabric plies are secured to each other along the transverse and longitudinal lines of attachment earlier referred to by thermal welding rather than by the use of stitching, as had conventionally been done. For each string of pocket springs, the pocket fabric is thermally weldable to itself so that the two plies of fabric of the folded strip in which the pockets are defined may be secured together without the necessity for stitching. In doing so, a stronger bond than is achieved when compared with sewing the same fabric material. At the same time, the elimination of any need for the thread and the sewing apparatus which was necessary to the manufacture of upholstery springs of this type. The utilization of thermally weldable materials provides a substantial simplification of the manufacture of superior springs. The manufacturing techniques disclosed in U.S. Pat. No. 4,234,983 are incorporated herein by way of reference.
In society, different people have different preferences when it comes to qualities in mattresses. For example, some people prefer a softer mattress and others prefer a harder mattress. It may be possible for a manufacturer to produce a soft mattress or a hard mattress. However, it is generally more difficult for a manufacturer to provide greater control over the firmness of the resultant mattress. For example, using the techniques disclosed in U.S. Pat. No. 4,234,983, a manufacturer could produce a soft mattress or a hard mattress by determining an appropriate a rate of springs for use in manufacturing the mattress core. However, U.S. Pat. No. 4,234,983 does not anticipate further techniques for controlling the firmness of the resultant mattress.
The above described problems are more pronounced when a mattress is to be shared by two people with different requirements for mattress firmness. This is particularly the case when the mattress is to be shared by a man and a woman having different body sizes, for example. In this situation, a mattress that is considered to have an adequate firmness by the larger of the two will invariably be considered too hard for the lighter of the two. It is difficult to find a single mattress that satisfies the requirements of both parties.
It is generally desirable to overcome or ameliorate one or more of the above mentioned difficulties, or at least provide a useful alternative.